The present invention relates to a charged particle beam apparatus such as a scanning electron microscope, and more particularly to a charged particle beam apparatus which tilts and emits a beam with respect to a specimen or to an ideal optical axis of the beam.
An inspection device and a measuring device using an electron beam are demanded to have high precision three-dimensional observation function in order to improve a yield of a three-dimensional device. A method of obtaining an image with a stage inclined has been used for three-dimensional observation using an electron microscope. However, it had problems that the reproducibility of throughput and tilt angle was degraded because mechanical movement was needed to tilt a stage or a column. A method is considered to use a deflector to tilt the beam in order to perform a three-dimensional measurement of the device without inclining the stage.
However, when beam tilt (deflection) is performed by the deflector, a deflection coma aberration and an off-axis chromatic aberration are generated, and beam diameter is increased. To eliminate the deflection coma aberration and the off-axis chromatic aberration which are generated at the time of beam deflection, it is necessary to produce an aberration of the same amount but of opposite sign with respect to the respective aberration generated by the objective lens by another optical element, and the following methods are known.
JP-A-2000-348658 (U.S. Pat. No. 6,452,175) discloses a method that mutually cancels off-axis chromatic aberrations which are generated before and after the lens by a two-stage deflector which is positioned in the objective lens field and deflects the beam in opposite directions.
WO01/33603 (U.S. Pat. No. 6,864,482) discloses a technology in which, when shifting a field of view (image shift) is performed by deflecting the beam, the off-axis chromatic aberration of an arbitrary direction generated at the objective lens when an image shift is performed, is corrected by causing chromatic dispersion by a Wien filter which is arranged on the optical axis on the electron source side away from the objective lens.
JP-A-2001-15055 (U.S. Pat. No. 6,614,026) discloses a method of compensating an off-axis chromatic aberration which is generated when a beam is tilted by causing a chromatic dispersion by an electromagnetic multipole. In addition, it also discloses a method of simultaneously cancelling out the off-axis chromatic aberration and the deflection coma aberration with a hexapole field added to the compensation unit.
JP-A-2006-54074 (U.S. Pat. No. 7,223,983) discloses a method of compensating chromatic aberration and spherical aberration, which are generated when the beam is tilted, by an aberration corrector by tilting the beam without moving an object point of the aberration corrector which is arranged on the electron source side away from the objective lens.
JP-A-2006-12664 (U.S. Pat. No. 7,355,174) discloses a method of adjusting to optical conditions under which off-axis chromatic aberration is made equal to 0 by setting the optical conditions so as to make a positional deviation equal to 0 generated when an excitation current is changed.